This invention is directed to display devices and, more particularly, to exposure display devices for single lens reflex cameras.
In general, two interrelated exposure components are involved in single lens reflex cameras, one or both of which may be displayed in the viewfinder of the camera. These exposure components are normally referred to as shutter speed and diaphragm value (f-stop). In single lens reflex cameras, regardless of whether or not they are manually controlled or automatically controlled, one of these components is preadjusted. This preadjustment informtion, plus information about the brightness of the object to be photographed and film sensitivity, defines the value of the other exposure component. For example, if the diaphragm value is preadjusted, then shutter speed is determined by the preadjustment value, object light and film sensitivity. In an automatic camera, the shutter speed is automatically set by the camera's electronic system in accordance with these parameters. In many manually adjusted cameras (or the manual mode of automatic cameras), a viewfinder display informs the operator of the necessary shutter speed adjustment and he adjusts the shutter speed accordingly. Conversely to the foregoing, if shutter speed is preadjusted, then diaphragm value is controlled and/or displayed.
In the past, a variety of methods and apparatus for displaying exposure information in the viewfinder of a single lens reflex camera have been proposed and used. These prior art methods and apparatus can be classified in two broad groups -- an analog group and a digital group. The analog group utilizes analog techniques and usually employs an ammeter whose needle position is controlled in accordance with information received by the camera. The digital group utilizes digital techniques and employs solid state display elements for displaying exposure information. Each group has its merits and demerits and an ultimate conclusion cannot be reached about which of these groups is superior to the other group. In this regard, the needle of an ammeter is not extremely rigid, making exposure devices using ammeters somewhat unreliable. Further, ammeter display devices are the source of a major portion of camera disorders. Moreover, ammeter display devices are not particularly suitable for use in cameras with automatic exposure control devices having wide exposure ranges, because their display range is limited to the maximum deflection angle of the ammeter needle. A still further disadvantageis that, because ammeter structures are relatively voluminous and occupy a large space within a camera housing, they prevent the formation of compact cameras.
In order to overcome the disadvantages of ammeter exposure display systems, a full-digital display has recently been proposed for inclusion in single lens reflex cameras. However, such systems present other problems. One of the major problems or disadvantages of digital display systems is their requirement for a relatively complicated large circuit when it is desired to provide displays for all currently employed shutter speeds. Another difficulty with digital display systems is the requirement that the operator of the camera be re-educated. That is, camera users are generally accustomed to conventional analog display systems employing an ammeter structure. In order for them to utilize digital displays, they must be re-educated. Re-education is necessary because it is essentially impossible to make the digital displays large enough to be easily viewed and because the display numerals vary frequently and hastily from one value to another value, whereby users have found it difficult to read out the required EV (exposure value).
Therefore, it is an object of this invention to provide a new and improved exposure display device.
It is a further object of this invention to provide a new and improved exposure display device for single lens reflex cameras.
It is another object of this invention to provide a new and improved exposure display device for single lens reflex cameras that eliminates many of the disadvantages of ammeter display systems, yet retains many of their advantages.
It is a still further object of this invention to provide a new and improved exposure display device for single lens reflex cameras that eliminates many of the disadvantages of digital display devices, yet retains many of their advantages.
It is yet another object of this invention to provide an exposure display device for single lens reflex cameras that incorporates many of the advantages of both analog display devices and digital display devices while eliminating many of the disadvantages of both devices.